There has been a trend in the U.S. automotive industry toward high performance, high RPM engines which, to achieve maximum performance and efficiency, are operated in the near borderline knock region. Unfortunately, knock detection is more difficult in the noisier environment of an engine at high RPM; and knock control apparatus with noise reduction circuitry designed for lower RPM engines, which can contain envelope detecting analog low pass filters and analog integrators, may introduce phase and group delays which make consistent and accurate knock detection at high RPM difficult.